1. Field of the Invention
The present invention relates to a compressor control system for an air conditioner, and particularly to a compressor control system for an air conditioner which improves the control of the operation of a rotary type compressor.
2. Description of the Related Art
According to most of generally-known air conditioners, air cooling/heating operation is carried out through a refrigeration cycle in which refrigerant alternately repeats condensation and evaporation, and in this refrigeration cycle the refrigerant is subjected to a high-temperature and high-pressure process and also compressed so that the refrigerant is provided with circulating power. A rotary or scroll type compressor is more frequently used to compress the refrigerant, and an induction motor or a DC motor is also more frequently used as an electric motor for these types of compressors. As one of these compressors is known a rotary type compressor 1 containing a single-phase induction motor which is driven by single-phase power as shown in FIG. 1.
According to the induction motor, voltage is applied to plural coils while varying the phase of the voltage among the coils, thereby generating a rotating magnetic field, and a rotator is driven by the rotating magnetic field thus generated. In the case of the single-phase induction motor, the phase of the power source is single, and thus the voltage of the power source is applied to a primary coil while a voltage which is advanced in phase by inserting a capacitor in series is applied to an auxiliary coil, thereby generating a rotating magnetic field. This type of induction electric motor is known as a capacitor run motor type, and it is frequently used. The rotating magnetic field generated by the above capacitor run motor is more unstable than that generated by a three-phase induction motor based on a three-phase alternating power source, and the rotational force induced is more inhomogeneous.
The single-phase induction electric motor will be described in more detail with reference to FIG. 1.
The single-phase induction motor of the compressor 1 is supplied with an alternating voltage of about 200 V from a power source unit 2. The operation (start, stop) of the compressor 1 is controlled on the basis of an operating signal from a controller 3. The controller 3 controls not only the compressor 1, but also the other parts of an air conditioner.
The voltage from the power source unit 2 is stabilized by a power converting device 4 comprising a transformer 5, a rectifying/smoothening circuit 6 and a voltage regulating circuit (constant-voltage circuit) 7, and the voltage thus stabilized is finally applied to the controller 3. When the voltage supply from the power source unit 2 is interrupted due to a power failure, a reset signal is output from the voltage regulating circuit 7 of the power converting device 4 to the controller 3 to reset the controller 3, whereby an operating signal output from the controller 3 to the compressor 1 is extinguished. The operating signal is used to actuate the compressor 1.
However, since an electrolytic capacitor is used for the rectifying/smoothening circuit 6 of the power converting device 4, the voltage supply from the voltage regulating circuit 7 to the controller 3 is continued for several hundreds msec from the occurrence of the power failure. Therefore, no reset signal is output from the voltage regulating circuit 7 to the controller 3, so that the controller 3 continues to operate and output the operating signal to the compressor 1. That is, the compressor 1 continues to rotate for the above time period.
Furthermore, the power supply from the power source unit 2 to the compressor 1 is interrupted simultaneously with the occurrence of the power failure, and a roller 8A of the compressor 1 continues to rotate in a normal direction A by the inertial force and finally stops as shown in FIG. 2. When the power failure occurs in the process of compressing refrigerant, the compressed refrigerant applies its repulsive force acting in the opposite (reverse) direction B to the normal direction to the roller 8A of the compressor 1 under the compression process indicated by a two-dotted chain line of FIG. 2.
In FIG. 2, reference numeral 8B represents a cylinder, reference numeral 8C represents a vane, and reference numerals 8D and 8E represent a suction port and a discharge port provided to the cylinder 8B.
In the case of a long-term (several hundreds msec or more) power failure, when the compressor 1 is in the refrigerant compressing process at the time of occurrence of the power failure, with the repulsive force induced by the compressed refrigerant, the compressor 1 starts to rotate in the reverse direction due to the interruption of the power supply to the compressor 1. However, during the long-term power failure, the voltage supply from the voltage regulating circuit 7 to the controller 3 is interrupted, and thus the reset signal is output from the voltage regulating circuit 7 to the controller 3 to reset the controller 3, so that the operating signal from the controller 3 to the compressor 1 is extinguished. Therefore, the reverse rotation of the compressor 1 is stopped.
On the other hand, in the case of a short-term (from several tens (about 40) msec to several hundreds msec or less) power failure, when the compressor 1 is in the refrigerant-compressing process at the time of occurrence of the power failure, the repulsive force induced by the compressed refrigerant causes the compressor 1 to start rotating in the reverse direction, however, the voltage supply from the voltage regulating circuit 7 to the controller 3 still continues during this power failure, so that no reset signal is output from the voltage regulating circuit 7 to the controller 3, so that the controller 3 continues to output the operating signal to the compressor 1. Accordingly, when the power is restored after the short-term power failure, the single-phase induction motor of the compressor 1 generates unstable rotational magnetic field, and the rotational force in the normal direction is weak, so that the compressor 1 continues to rotate in the reverse direction.
The reverse rotation of the compressor 1 causes increase of the pressure in the compressor 1 and heating, and lubricant oil in the compressor 1 is deteriorated, finally resulting in failure of the compressor 1.
Usually, the compressor 1 is provided with a device for monitoring the pressure at the exit thereof or the operation current thereof to prevent the failure of the compressor 1. In the reverse rotation state of the compressor, there is little variation from the normal state in the pressure at the exit and the operation current, so that the reverse rotation phenomenon cannot be detected by using the monitoring device described above. Further, even when a thermostat for detecting the increase of temperature or the like is provided to the coil of the electric motor of the compressor, it takes long time until the temperature of the coil increases to a temperature at which the thermostat operates, and thus the compressor 1 may fail due to the reverse rotation of the compressor 1.
Besides, when the reset signal is output from the voltage regulating circuit 7 of the power converting device 4 to the controller 3, depending on the power occurrence manner of the power source unit 2, some dispersion may occur in reset time in which the reset of the controller 3 is completed, and particularly when the voltage of the power source unit 2 is reduced, the voltage regulating circuit 7 may erroneously output a reset signal to the controller 3.